1. Field of the Invention
This invention relates to compound archery bows. It is particularly directed to an improved rigging system for such bows.
2. State of the Art
Compound archery bows commonly carry assemblies of pulley members (usually called “eccentrics” or “cams”) eccentrically mounted on axles in association with respective bow limbs. These limbs extend in opposite directions from a grip (usually comprising a central portion of a handle riser). The rigging for compound bows includes a bowstring trained around the pulley members of the system, the string being received by grooves or other functionally equivalent features at the perimeters of the pulleys. The eccentric pulley assemblies are conventionally mounted to rotate (pivot) on an axle within a notch at the distal end of the limb, or within a bracket structure carried by the limb tip. The eccentrics include one or more pivot holes substantially offset from center, whereby to provide for a reduction in the holding force felt at the nocking point of the bowstring, as the string is moved to its fully drawn condition.
Compound bows and various exemplary riggings, including pulley assemblies, are described by U.S. Pat. Nos. 3,486,495; 3,990,425; 4,748,962; 4,774,927; 4,967,721 and 6,763,818, the disclosures of which are incorporated as a portion of this disclosure.
The rigging for compound bows typically includes cable segments, which may be end stretches extending from an integral bowstring. More often, however, the cable segments are separate elements, each connecting at one end, directly or indirectly, e.g., through structure associated with the pulley assembly, to a terminal end of the bowstring. The remaining (distal) ends of the cable segments are conventionally connected to the opposite bow limb or structure, such as the pivot axle mount of the pulley assembly carried by that limb. In any case, each cable segment includes one or two stretches oriented approximately parallel the bowstring. “Approximately parallel,” is intentionally fluid in context, merely recognizing that the cable segments and bowstring all extend generally across, but out of contact with, the handle riser portion of the bow between the pulley assemblies, or other structure, carried by the respective bow limbs. All of the cable stretches are thus confined within a space defined by reference planes straddling the handle riser and containing the bowstring. The cable stretches are commonly positioned to one side of the bowstring to avoid interference with the nocking point of the bowstring. It is common practice to mount cable guard rods or other structures to the handle riser. These structures are positioned physically to hold the cables away from the plane of travel of the bowstring. Compound bows have sometimes been configured to position cables on opposite sides of a bowstring so that an arrow may be cast in the plane of the bowstring between cable stretches.
With a compound bow oriented in its normal position of use, it is conventional to consider the bow as being oriented vertically. Unless otherwise stated, the bows referred to in this disclosure are assumed to be in this “vertical” orientation. The handle riser is thus considered to have an “upper end,” a “lower end” and a central grip portion. The limb extending from the upper end of the handle riser may be referred to as “a first limb” or the “upper limb,” in either case terminating in an “upper limb tip.” Corresponding terminology is applied to the “second limb,” which extends from the lower end of the handle riser. The bowstring is assumed to travel in a plane (“operating plane”) of travel between a fully drawn condition and braced or at rest condition. Cable stretches may be viewed as being positioned to the left or right of the plane of travel of the bowstring, recognizing that in some rigging systems, a cable stretch may be to one side of that plane of travel along the first limb and to the opposite side of that plane of travel as the stretch proceeds to its point of attachment at the second limb. The geometry of a compound bow inherently lacks bisymmetry with respect to the operating plane of the bowstring. The relative magnitudes of forces applied by the bowstring and cable stretches changes, often irregularly, as the nocking point is drawn or an arrow is launched. The variety of rigging configurations present in the field is explained in part by different approaches taken by bow designers with respect to the balancing of forces unevenly applied to limb tips, axles, limb mountings and other bow components by the cable stretches under actual use conditions.
A troublesome characteristic of the rigging systems offered by commercial compound bows is the inherently unequal application of force to opposite sides of the mounting axles of the pulley assemblies as the bowstring is drawn. As a general matter, riggings that position all of the cables to one side of the bowstring inevitably apply cable forces to the same side of the string groove. The assemblies thus tend to lean, tip, or twist with respect to the operating plane of the bowstring. Various terminal cable end configurations have been proposed to distribute the force load applied to the axles or limb tips in an effort to ameliorate this problem. One such configuration is that commonly referred to as a “yoke” or “Y harness.” In that arrangement, the terminal, or anchor, end of a cable is divided into two strands, which extend to opposite sides of a pulley assembly, thereby evenly distributing the force applied by that cable to its respective attachment points.
Proper operation of a compound bow typically requires periodic “tuning;” that is, synchronization of the pulley members. The pulley assemblies must be synchronized in their rotation so that the mechanical advantages developed through the two assemblies change at the same rate and to the same degree. Over a period of use, for various reasons, including stretching of the bowstring, compound bows typically migrate out of tuned condition. Re-tuning of the bow requires time consuming and technically demanding adjustments of the rigging. A number of efforts have been made to modify the rigging of compound bows to overcome or reduce the tuning requirement of such bows. These efforts have had little practical success. The persistent need for tuning and re-tuning is believed to be a major impetus for the wide acceptance of single cam bows. Single cam bows are believed by most archers to require much less effort to keep in tune, although the performance of the single cam configuration is less desirable in other respects than is the performance of conventional compound bows.
U.S. Pat. No. 3,990,425 proposes a rigging system that cross-couples the pulley assembles of a compound bow so that they are constrained to move in unison, thereby providing a self-tuning function to the bow. To the extent that this expedient has been incorporated into commercial compound bows, the riggings have tended to exacerbate the inherent characteristic of pulley assemblies to twist (or lean) on their axle mounts. The riggings employed to date in cross-coupled bows apply cable force to the limb tips in a fashion that imparts a twisting moment to the mounting axles of the pulley assemblies. The '425 patent discloses pulley assemblies in which all of the working grooves are circular and in which cross coupling is accomplished through an anchoring arrangement which inherently imparts a leaning moment to the pulley assemblies. Specifically, the cables are all disposed to one side of the bowstring.